Image forming apparatus and image forming method

Abstract

An image forming apparatus including: an outputting section to output a chart which has a gradation pattern in a low-density area, the gradation pattern including patches, each of the patches having a density; a reading section to read-in the density of each of the patches; a calculating section to calculate, based on the density, an adjusting value to conduct a gamma correction; and an output adjusting section to conduct an adjustment of an output in the low-density area based on the calculated adjusting value.

1. An image forming apparatus comprising:
 an outputting section to output a chart which comprises a gradation pattern in a low-density area, the gradation pattern including patches, each of the patches having a density; 
 a reading section to read-in the density of each of the patches for obtaining an input-output characteristics; 
 a calculating section to calculate an adjusting value to adjust the output in the low-density area of a low-density correction curve, wherein the low-density correction curve has output values corresponding only to input values of not greater than a half of maximum input value of a gradation correction curve; and 
 an output adjusting section to conduct an adjustment of an output in the low-density area based on a the gradation correction curve for totally correcting gradation characteristics, and on the low-density correction curve including the adjusting value as a parameter, 
 wherein the calculating section extracts, from the input-output characteristics, a referential input value corresponding to an input value where a color density starts to rise in a gradation of the low-density area, receives a target input value regarding the input value where the color density starts to rise, and calculates an offset value to adjust the output in the low-density area as the adjusting value, so as to satisfy a relation of:
     B′+C′=B+C;    
 where B′ represents an output value when the referential input value is inputted to the gradation correction curve, 
 C′ represents an output value when the referential input value is inputted to the low-density correction curve before applying the adjusting value, 
 B represents an output value when the target input value is inputted to the gradation correction curve, and 
 C represents an output value when the target input value is inputted to the low-density correction curve after applying the adjusting value. 
 
 
     
     
       2. An image forming apparatus comprising:
 an outputting section to output a chart which comprises a gray gradation pattern including patches, each of the patches having a density; 
 a reading section to read-in the density of each of the patches for obtaining an input-output characteristics; 
 a calculating section to calculate an adjusting value to adjust the output in a low-density area of a low-density correction curve; and 
 an output adjusting section to conduct an adjustment of an output in the low-density area based on a gradation correction curve for totally correcting gradation characteristics, and on the low-density correction curve including the adjusting value as a parameter, 
 wherein the calculating section extracts, from the input-output characteristics, a referential input value corresponding to a position where a distance from the referential gray position being minimum, receives an target input value for adjusting gray balance as a target value, and calculates an offset value to adjust the output in the low-density area as the adjusting value, so as to satisfy a relation of: B′+C′=B+C
 where B′ represents an output value when the referential input value is inputted to the gradation correction curve, 
 C′ represents an output value when the referential input value is inputted to the low-density correction curve before applying the adjusting value, 
 B is an output value when the target input value is inputted to the gradation correction curve, and 
 C represents an output value when the target input value is inputted to the low-density correction curve after applying the adjusting value. 
 
 
     
     
       3. The image forming apparatus of  claim 1 , wherein the chart comprises a random pattern in which plural patches are randomly arranged. 
     
     
       4. The image forming apparatus of  claim 1 , further comprising:
 a memory section to memorize an allowable range of the output value corresponding to the target value; and 
 an adjusting value judgment section to read-in an image outputted through the correction after the adjustment, and judge whether an output of the image read-in falls within the allowable range of the output value corresponding to the target value, and finalize the adjustment when the output falls within the allowable range. 
 
     
     
       5. The image forming apparatus of  claim 4 , wherein when the adjusting value judgment section judges that the output falls out of the allowable range, the adjustment is conducted again,
 wherein the image forming apparatus further comprises an adjustment number of times judgment section which finalize the adjustment when adjustment number of times exceeds a preset upper limit. 
 
     
     
       6. An output correcting method of an image forming apparatus for correcting an output image based on a gradation correction curve to totally correct gradation characteristics of the image forming apparatus and a low-density correction curve to correct gradation characteristics in a low-density area, wherein the low-density correction curve has output values corresponding only to input values of not greater than a half of maximum input value of a gradation correction curve, the output correcting method comprising the steps of:
 outputting a chart which comprises a gradation pattern in a low-density area, the gradation pattern including patches, each patch having a density; 
 reading-in the density of each patch of the chart outputted, for obtaining an input-output characteristics; 
 extracting, from the input-output characteristics, a referential input value corresponding to an input value where a color density starts to rise in a gradation of the low-density area; 
 receiving a target input value regarding an input value where the color density starts to rise; 
 calculating an offset value for adjusting an output in the low-density area, as an adjusting value of the low-density correction curve, so as to satisfy a relation of:
     B′+C′=B+C    
 
 where B′ represents an output value when the referential input value is inputted to the gradation correction curve, 
 C′ represents an output value when the referential input value is inputted to the low-density correction curve before applying the adjusting value, 
 B represents an output value when the target input value is inputted to the gradation correction curve, and 
 C represents an output value when the target input value is inputted to the low-density correction curve after applying the adjusting value; and 
 adjusting the output in the low-density area based on a the gradation correction curve for totally correcting gradation characteristics, and on the low-density correction curve including the adjusting value as a parameter. 
 
     
     
       7. The output correcting method of  claim 6 , further comprising the steps of:
 outputting second chart comprising a gradation pattern in the low-density area, after the step of adjusting the output; and 
 judging, after reading-in the second chart outputted, whether a read-in value falls within an allowable range of the output value corresponding to the target value memorized previously. 
 
     
     
       8. The output correcting method of  claim 7 , further comprising the steps of:
 finalizing the adjustment when the read-in value is judged to fall within the allowable range; 
 re-adjusting the output value by repeating the calculating step, the outputting second chart step, and the judging step, when the read-in value is judged to fall out of the allowable range; and 
 finalizing the adjustment when an adjustment number of times exceeds a preset upper limit. 
 
     
     
       9. The output correcting method of  claim 6 , wherein the chart comprises a random pattern in which plural patches are randomly arranged. 
     
     
       10. An output correcting method of an image forming apparatus for correcting an output image based on a gradation correction curve to totally correct gradation characteristics of the image forming apparatus and a low-density correction curve to correct gradation characteristics in a low-density area, wherein the low-density correction curve has output values corresponding only to input values of not greater than a half of maximum input value of a gradation correction curve, the output correcting method comprising the steps of:
 outputting a chart which comprises a gray gradation pattern, the gradation pattern including patches, each patch having a density; 
 reading-in the density of each patch of the chart outputted, for obtaining an input-output characteristics; 
 extracting, from the input-output characteristics, a referential input value corresponding to a position where a distance from the referential gray position being minimum, 
 receiving an objective input value for adjusting gray balance as a target input value; 
 calculating an offset value for adjusting an output in the low-density area as an adjusting value of a low-density correction curve, so as to satisfy a relation of:
     B′+C′=B+C    
 where B′ represents an output value when the referential input value is inputted to the gradation correction curve, 
 C′ represents an output value when the referential input value is inputted to the low-density correction curve before applying the adjusting value, 
 B represents an output value when the target input value is inputted to the gradation correction curve, and 
 C represents an output value when the target input value is inputted to the low-density correction curve after applying the adjusting value; and 
 adjusting the output in the low-density area based on the gradation correction curve for totally correcting gradation characteristics, and on the low-density correction curve including the adjusting value as a parameter.